Method and apparatus for measuring oxygen content

ABSTRACT

A method and apparatus for measuring the oxygen content in a closed target space, particularly for monitoring inertization levels in an inert gas device for fire prevention and/or fire extinguishing. Toward the aim of proposing a method for measuring the oxygen content in a target space with which an effective, certain, and representative determination of the oxygen concentration can be achieved for an optimally small expenditure in instrumentation and signal processing, the method provides that air samples are drawn from the target space and the oxygen concentration of the air samples is determined. An apparatus is equipped with a suction pipe system for sucking the air sample from the target space through various holes so that it can carry out the method.

BACKGROUND

The present invention relates to a method for measuring the oxygencontent in a sealed target space, particularly for monitoringinertization levels in an inert gas device for fire prevention and/orfire extinguishing, and to a device for carrying out the method.

In closed rooms containing equipment that is sensitive to water, such asDP areas, electrical switching and distribution rooms, or storage areascontaining high-value goods, what are known as inertization methods areincreasingly being utilized to reduce the risk of fires and toextinguish them. The extinguishing effect produced by this technique isbased on the principle of oxygen displacement. As is generally known,normal ambient air consists of 21% oxygen, 78% nitrogen, and 1% othergasses by volume. In order to extinguish and prevent fires, the inertgas concentration in the relevant space is elevated, and so theproportion of oxygen is reduced, by infusing an inert gas such as purenitrogen that displaces oxygen. Many substances no longer burn when theoxygen level drops below 15–18% by volume. It may be necessary to lowerthe oxygen level further to 12%, for example, depending on thecombustible materials in the relevant room.

Some known systems employ an inertization method with which a fire canbe effectively extinguished given an optimally small storage capacityfor the flasks of inert gas. According to this method, the oxygencontent in the closed room is lowered to a base inertization level,(e.g., 16%) and in the event of fire, a very rapid full inertizationoccurs (e.g., an inertization of 12% or lower).

An inert gas device for fire prevention and/or fire extinguishing forcarrying out the cited inertization method includes the followingcomponents: an oxygen meter for measuring the oxygen content in themonitored target space; a fire detector for detecting a combustionparameter in the air of the target space; a control for evaluating thedata of the oxygen meter and the combustion parameter detector andcontrolling the running of the inertization process; and an apparatusfor producing inert gas and abruptly infusing it into the target space.

The term combustion parameter refers to physical quantities thatunderlie measurable changes in the environment of an incipient fire(e.g., the ambient temperature, the proportion of solids, liquids, orgas in the ambient air (formation of smoke in the form of particulates,aerosols, or vapor) or the ambient radiation).

The oxygen meter serves for setting the base inertization level in thetarget space. If a threshold oxygen concentration value is exceeded,such as due to a leak in the target space, the control sends a commandto a separate system to infuse inert gas into the space, so that theoxygen proportion is reduced. The oxygen meter signals when thethreshold value of the base inertization level has been reached again.The position of the base inertization level therein depends onproperties of the room. But if the detector for combustion parameterssenses a combustion parameter, however, the system receives a command toflood the room with inert gas until the oxygen concentration in thetarget space is reduced to a specified full inertization level.

The measuring of the oxygen content in the target space is important fora reliable control of the method in this type of inert gas device forfire prevention and/or fire extinguishing. According to the prior art,the oxygen concentration in the target space is measured by point shapedoxygen sensors, which transmit the measurement values of the oxygencontent to the control in the form of an analog signal. It is common toutilize 4–20 mA current interfaces, where 4 mA corresponds to aconcentration of 0% oxygen, and 20 mA corresponds to the end of themeasurement range (e.g., 25% oxygen). The disadvantage of utilizingpoint shaped oxygen sensors is that a greater number of such sensors areneeded in the target space in order to get a representative reading ofthe oxygen content in the air in the room. That requires correspondinglycostly cable connections between the individual sensors that aredistributed in the target space and the actual control. Furthermore, thecontrol requires a correspondingly high number of analogous interfaces.This requires a particularly large and particularly expensive hardwareoutlay.

An exceptionally disadvantageous aspect turns out to be that the controlmust continuously process a large number of signals. In particular,forming average values, estimating errors, and comparing to presetthreshold values require routines, which are absolutely indispensablefor controlling the inertization process. Only with the aid of theprocessed data of the oxygen sensors is it possible to drive the systemfor infusing inert gas, a fresh air supply, or a fan for air circulationin the target space. The signal processing in the control is thereforevery intensive and requires a high complexity of software.

SUMMARY

The present invention proposes a method for measuring the oxygen contentin a target space with which it is possible to determine the oxygenconcentration effectively, reliably, and in representative fashion, andwith an optimally small outlay for instrumentation and signalprocessing. This is achieved by a method for measuring oxygen contentincluding taking an air sample from the target space by means of aseries of suction holes of a suction pipe system, so that the oxygenconcentration of the air sample can then be determined by means of anoxygen detector.

The present invention provides a number of benefits for measuring theoxygen content in a target space. Air samples from various suction holesare mixed by suction through holes in the suction pipe system. Thus, theoxygen concentration of the air sample automatically corresponds to anaverage value of the oxygen concentration of the target space, and thecostly average value formation is omitted from the signal processing ina control. In a simpler embodiment, software for evaluating themeasurement values can even be omitted. Furthermore, the monitoredvolume (i.e., the measured volume), is substantially larger than in thecase of oxygen sensors that are configured in points as in the priorart. This brings particular cost advantages in the purchasing,installation, and maintenance of the device for measuring the oxygencontent in the target space and ultimately of the overall inert gasdevice for fire prevention and/or fire extinguishing.

The present invention also includes a device for carrying out the abovemethod that includes at least one suction pipe system for drawing an airsample from the monitored target space through various holes. The devicerealizes the combination of the inventive method with an oxygen meter inan ideal fashion. Benefits are gained particularly by the ability toforgo the utilization of a plurality of point shaped oxygen sensors inthe target space. Instead, at least one suction pipe system is providedfor drawing an air sample from the monitored target space throughvarious suction holes. That way, complicated cable connections betweenthe former point shaped oxygen sensors and the control can also beomitted. An analog interface must still be provided in the control forthe oxygen meter, but this can be realized with a small hardware outlay.Furthermore, the signal processing in the control is substantiallysimpler, since it is no longer necessary to process a large number ofsignals from individual oxygen sensors. As a result, the software forsignal processing can also be constructed correspondingly simple. It istherefore possible to measure the oxygen content at little expense interms of instrumentation and signal processing, which brings economicbenefits particularly in the purchase and maintenance of the inert gassystem as a whole.

Following the determination of the oxygen concentration of the drawn airsample by the oxygen sensor, the oxygen measuring method includescomparing the measurement value of the oxygen concentration of the airsample to fixed threshold values in the oxygen sensor, and, in the casewhere the fixed threshold value is exceeded, reducing the oxygenconcentration by infusing inert gas into the target space. Thus, theinertization method is adapted for possible leaks in the target space bymeans of the continuous measuring of the oxygen content. A benefit ofthis development is the existence of a separate “intelligence,” so tospeak, in the inventive oxygen measuring method, in the sense that themethod performs a comparison with predetermined threshold values of itsown accord. A signal is sent to the control in a central unit only whena threshold value is crossed. This substantially reduces, not only thedata traffic between the device for carrying out the inventive oxygenmeasuring method and the control of the inert gas device for fireprevention and/or fire extinguishing, but also substantially reduces thesignal processing in the control. With this “distributed intelligence,”signal processing can be divided between the control and the oxygensensor that is connected to it. This makes possible a substantialreduction in the software outlay, and particularly the purchase priceand the maintenance outlay of the control of an inert gas device forfire prevention and/or fire extinguishing.

A detector for fire parameters may be utilized in the disclosed methodfor measuring the oxygen content in the target space. This detectorsends a signal for full inertization in the event of fire. Thisdevelopment represents the procedural implementation of the combining ofa known aspirative fire detector with the inert gas extinguishingtechnique. An aspirative fire detector is a fire detector that activelydraws a representative subvolume of air from the room at a number oflocations via a suction pipe system, conduit system, or duct system andthen conducts these subvolumes to a detector for detecting a fireparameter. With the integration of the detector of fire parameters intothe device for carrying out the disclosed method, an aspirative firedetector is created in addition to the oxygen measuring device. It isbeneficial that existing components can be accessed for realizing thisaspirative fire detector. The target space can thus be equipped with anaspirative fire detector, thereby improving the fire detection, withoutadditional outlay.

In another example of the disclosed method, the fire parameters sensedby the detector are smoke in the form of particulates, aerosols, orvapor, and at least one combustion gas. That way, the fire detector thatis equipped with the disclosed oxygen meter reacts with particularsensitivity to the parameters that are typical of a fire. A fire canthus be detected in its incipient stage, and the inert gas device forfire prevention and/or fire extinguishing can be alarmed.

One example of the inventive oxygen meter provides that the combustiongas that is sensed in the detector is CO or CO₂. The advantage of thisembodiment in particular is that the fire detector is especiallysensitive to fire parameters and is also able to distinguish between anactual fire and cigarette smoke or other smoke-like quantities that arenot characteristic of fire. Alternative embodiments are of course alsoimaginable.

In another example, the measurement of the air quality by a CO or CO₂sensor is integrated into the method, and the fresh air supply of thetarget space is controlled in dependence on the signal of the CO or CO₂sensor. The advantages that are discussed above in connection with theoxygen sensor are also brought to bear here. In particular, thisadvantageous embodiment forgoes the utilization of a plurality of CO orCO₂ sensors that are distributed in the target space and that measurepointwise, as well as the correspondingly large hardware and softwareoutlay in the control for processing the signals.

Yet another example determines the oxygen concentration by means of areference oxygen sensor. This is done independently from the measuringof the above cited oxygen sensor. The reference oxygen sensor ispermanently disposed in the air stream of the air sample that is drawn.For example, the reference oxygen sensor could be located in theimmediate vicinity of the oxygen sensor. The measurement value of theoxygen concentration that is acquired by means of the reference oxygensensor is then compared to the measurement value of the oxygenconcentration that was registered at the same time by the oxygen sensorin the air stream. It is provided that a disturbance signal is emittedif the comparison of the two measurement signals indicates that theoxygen concentration value that was acquired by the oxygen sensordeviates from the oxygen concentration value acquired by the referenceoxygen sensor deviates more than a previously defined tolerance value.The comparison of measurement values and the output of the disturbancesignal can occur in and by means of the oxygen sensor or the referenceoxygen sensor. Alternative solutions are of course also imaginable.

In another example, it is further provided that the reference oxygensensor, as opposed to the oxygen sensor, is normally off. The referenceoxygen sensor is switched on at regular intervals, such as once a day oronce a week. Following activation, a minimum heating time is allowed topass before the oxygen concentration in the air stream is determined.The activation process could occur with the aid of a signal that isgenerated by a clock timer. On the other hand, it would also beimaginable for the activation to occur at the push of a button, forinstance in maintenance operations. Premature aging of the referenceoxygen sensor can be prevented particularly easily by its being on onlytemporarily.

It is particularly beneficial when the disturbance signal, which isoutput when the comparison of the two measurement values indicates thatthe oxygen concentration value acquired by the oxygen sensor deviatesfrom the oxygen concentration value acquired by the reference oxygensensor by more than a previously defined tolerance value, is utilized tothe effect that the reference oxygen sensor remains on permanently and,therefore, continuously delivers measurement values of the oxygenconcentration of the drawn air sample. These measurement values are thenevaluated instead of those of the oxygen sensor. Measurementuncertainties that are caused by the aging of the oxygen sensor when itis continuously driven can thus be eliminated.

According to an example of a device, inertization levels in the targetspace are set by a control, which also controls the fresh air supply anda fan, whereby at least one oxygen sensor is provided for measuring theoxygen concentration in an air sample that is drawn from the targetspace, and at least one detector is provided for detecting fireparameters in an air sample drawn from the target space by one of thesuction pipe systems. Such a device is particularly easy to realize, inwhich the measuring components that are utilized in the inert gas devicefor fire prevention and/or fire extinguishing are utilized only foranalyzing the air sample drawn from the target space.

At least one CO or CO₂ sensor for measuring the air quality in an airsample drawn from the target space by one of the suction pipe systems isexpediently provided. Thus, the air quality can also be monitored by theinventive inert gas device for fire prevention and/or fireextinguishing.

An oxygen sensor and a detector for detecting fire parameters and/or aCO or CO₂ sensor are integrated in a suction pipe system. The number ofcomponents that are utilized in the inert gas device for fire preventionand/or fire extinguishing can thus be reduced. This brings additionaleconomic benefits in the purchase, installation and maintenance of aninert gas device for fire prevention and/or fire extinguishing.

In an example, electrochemical cells consisting of zirconium dioxide areutilized as oxygen sensors. Zirconium dioxide based oxygen sensors areknown from automotive technology, where they are used in catalyticconverters to measure the oxygen content in exhaust gasses. The sensorsare considered reliable, sensitive, sturdy and low-maintenancecomponents. The disclosed device can be realized particularlycost-effectively if standard components are utilized in the inventivedevice.

In a further example, it is provided that, besides the oxygen sensor, areference oxygen sensor is utilized for measuring the oxygenconcentration of the air sample that is drawn from the target space.This serves as a reference relative to the oxygen sensor and liescontinuously in the air stream, though the sensor is normally off. Thisprevents the aging of the reference oxygen sensor. The sensor isactivated at regular intervals (e.g., once a day or once a week). Thesignal for activating the reference sensor is generated by a clocktimer, for example. It can also be generated at the push of a button,for instance for maintenance operations. Following the activation of thereference oxygen sensor, the minimum heating time is allowed to pass.Then the two measurement values of the oxygen sensor and the referencesensor are compared. If the difference between the two values is largerthan a predetermined threshold, a disturbance is signaled, and thereference oxygen sensor is no longer switched off. Its measurementvalues are evaluated instead of those of the aged oxygen sensor.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a schematic block diagram of a device for measuringthe oxygen content in an inert gas device for fire prevention and/orfire extinguishing.

FIG. 2: illustrates a schematic representation of a device for measuringthe oxygen content in a closed target space.

DETAILED DESCRIPTION OF THE PRESENT EXAMPLES

FIG. 1 represents a schematic block diagram of a device for measuringthe oxygen content in an inert gas device for fire prevention and/orfire extinguishing 6. The inert gas device for fire prevention and/orfire extinguishing 6 serves to prevent and extinguish fires in theclosed target space 10. Two suction pipe systems 1 for sucking airsamples through various holes 2 are provided in the target space 10. Thesuction pipe systems 1 are each equipped with a suction sensor 8 inwhich the air samples from the target space 10 are conducted to anoxygen sensor 3 and to a detector 4 for detecting fire parameters,namely a CO or CO₂ sensor 5. In the device of FIG. 1, two suction pipesystems 1 are represented, one of which is mounted below the ceiling ofthe target space 10 at a distance of up to 1 m therefrom as warranted,and the other of which is mounted at breathing height, i.e.,approximately 1.5 m above the floor.

The oxygen sensor 3 a determines the oxygen concentration of therespective air sample and compares the measurement value to fixedthreshold values. If a fixed threshold value is exceeded, the oxygensensor 3 a sends a signal to a control 7 over a data line, whicheffectuates an infusion of inert gas into the target space 10 and areduction of the oxygen concentration. For that purpose, the control 7signals an apparatus for producing and infusing inert gas 6 to performan inertization of the target space 10.

Based on the continuous drawing of air samples from the target space 10by the aspirative suction device, the oxygen content of the air in theroom is continuously measured in the oxygen sensor 3 a. As soon as theoxygen concentration of the continuously drawn air sample in the oxygensensor 3 a matches a fixed threshold value, the control 7 receives acorresponding signal to discontinue inertization.

In the example represented in FIG. 1, in addition to smoke in the formof particulates, aerosols, or vapor, at least one combustion gas such asCO or CO₂ is also sensed in the detector 4 for detecting fireparameters. By utilizing at least two different fire parameters that canindependently establish the presence of a fire in the target space 10,it is possible to realize an optimal redundancy and a correspondingfail-safety of the inert gas device for fire prevention and/or fireextinguishing 6. In particular, the detector 4 is also able todistinguish between an actual fire and cigarette smoke or similarsmoke-like quantities that are not characteristic of fire.

In another suction pipe system 1 according to FIG. 1, a CO or CO₂ sensor5 and a detector 4 for detecting fire parameters are integrated in thesuction sensor. The CO or CO₂ sensor 5 monitors the air quality of thetarget space 10 by determining the CO or CO₂ content of the air samplethat is drawn by the suction pipe system. If the air quality of thetarget space 10 no longer corresponds to the expected standards, thesensor 5 signals this to the central control 7, which drives a fan 9 forair circulation, or respectively, fresh air supply 11. If a sufficientlyimproved air quality is subsequently measured, the fan 9 or fresh airsupply 11 then switches off again.

It is also possible to integrate several different sensors in a suctionsensor 8, for instance a CO or CO₂ sensor 5 in combination with adetector 4 for detecting fire parameters but also an oxygen sensor 3 ain combination with one of the other sensors 4 or 5 cited above.

Besides the oxygen sensor 3 a, a reference oxygen sensor 3 b may be alsoutilized for measuring the oxygen concentration of the air sample drawnfrom the target space 10. This serves as a reference relative to theoxygen sensor 3 a and lies in the air stream at all times but isnormally switched off. This prevents the aging of the reference oxygensensor 3 b. The sensor 3 b is switched on at regular intervals (e.g.,once a day or once a week). The signal for switching on the referenceoxygen sensor 3 b is generated by a clock timer. It can also begenerated at the push of a button, for instance in maintenanceoperations. Following the activating of the reference oxygen sensor 3 b,a minimum heating time is allowed to pass. The two measurement values ofthe oxygen sensor 3 a and the reference sensor 3 b are then compared. Ifthe difference between the two measurement values is greater than adefined threshold, a disturbance is signaled, and the reference oxygensensor 3 b is no longer switched off. Its measurement values areevaluated instead of those of the aged oxygen sensor 3 a.

FIG. 2 is a schematic representation of another exemplary device formeasuring the oxygen content in a closed room 10. In this example, thesuction pipe system 1 is attached beneath the ceiling of the target room10 by means of pipe straps 12. Air is drawn from the target space 10through the holes 2 in the suction pipe system 1. To that end, a suctionunit 13 that is integrated in the suction sensor 8 is utilized. Thesuction unit 13 and the suction pipe system 1 are monitored by means ofan air stream sensor 14 which is disposed at the end of the suction pipesystem 1.

After passing the air stream sensor 14, the air sample passes the oxygensensor 3 a. The oxygen sensor 3 a measures the oxygen concentration ofthe air sample, which represents an average value of the oxygenconcentration of the air of the target space 10. The average value iscompared to threshold values in the oxygen sensor 3 a. If the thresholdvalues are exceeded, the oxygen content in the air of the target space10 is too high to prevent a fire reliably. At the appearance of thesignal over a first threshold value, the control 7 drives the devicethat generates the inert gas and infuses the inert gas into the targetspace 10 (i.e., a generator).

If the oxygen content continues to rise, this indicates a defectivegenerator that cannot infuse inert gas into the space 10. At theappearance of the signal over a second threshold value, the control 7signals disturbance.

If the values are below the threshold values, a full inertization is nottriggered. At the appearance of the signal under a first thresholdvalue, the control 7 stops the generator because the desired oxygencontent has been achieved.

If the oxygen content continues to drop, this indicates a defectivegenerator that is no longer stopping the infusion of inert gas into thetarget space 10. At the appearance of the signal below a secondthreshold value, the control 7 signals disturbance.

If the oxygen content falls below a value that is dangerous to humans,personal safety measures are initiated. At the signal below a thirdthreshold value, the control 7 triggers personal safety measures such asthe evacuation of the room or the blocking of entry.

Instead of the oxygen sensor 3 a, a CO or CO₂ sensor 5 and/or a detector4 for detecting fire parameters can be utilized in the suction sensor 8.

Although preferred examples of the methods and apparatus have beendisclosed for illustrative purposes, those of ordinary skill in the artwill appreciate that the scope of this patent is not limited thereto. Onthe contrary, this patent covers all methods and apparatus found withinthe scope of the appended claims.

1. A method for measuring the oxygen content in a closed target spacefor monitoring inertization levels in an inert gas device forcontrolling fire, the method comprising the steps of: drawing an airsample from the target space with one or more suction holes of a suctionpipe system; determining a first measurement value of the oxygenconcentration in the drawn air sample using an oxygen sensor;determining a second measurement value of the oxygen concentration inthe drawn air sample using a reference oxygen sensor, wherein thereference oxygen is switched on at regular time intervals during thestep of determining the second measurement value to prevent aging of thereference oxygen sensor; comparing the first measurement value to thesecond measurement value; and issuing a disturbance signal from one ofthe oxygen sensor or the reference oxygen sensor when deviation of thefirst measurement value from the second measurement value exceeds apredetermined amount.
 2. A method as defined in claim 1, furthercomprising: comparing, in the oxygen sensor, the first measurement valueof the oxygen concentration of the air sample to a fixed thresholdvalue; and lowering the oxygen concentration by the infusion of inertgas into the target space when the threshold value is exceeded.
 3. Amethod as defined in claim 1, further comprising: measuring fireparameters in the drawn air sample with a detector; and sending a signalfrom the detector for full inertization of the target space when a fireparameter is detected.
 4. A method as defined in claim 3, wherein thefire parameters that are detected in the detector include at least oneof smoke in the form of particulates, aerosols, vapor, and at least onecombustion gas.
 5. A method as defined in claim 4, wherein thecombustion gas detected in the detector is CO or CO2.
 6. A method asdefined in claim 1, further comprising: monitoring CO and/or CO2 contentin the drawn air sample with a CO and/or CO2 sensor; and supplying freshair to the target space dependent on a measurement value of the COand/or CO2 content.
 7. A method as defined in claim 2, furthercomprising: following the issuing of the disturbance signal,continuously determining the oxygen concentration in the air sample withthe reference oxygen sensor, whereupon additional evaluation of thefirst measurement value of the oxygen concentration is performed withthe aid of the second measurement value that is determined by thereference oxygen sensor instead of the first measurement valuedetermined by the oxygen sensor.
 8. An apparatus measuring the oxygencontent in a closed target space of an inert gas device for controllingfire in a closed room, the apparatus comprising: an inert gas device; atleast one suction pipe system configured to suck an air sample from thetarget space through various holes; an oxygen sensor to measure oxygenconcentration in the air sample that is drawn from the target space anddetermine a first measurement value; and a reference oxygen sensor thatmeasures oxygen concentration in the air sample that is drawn from thetarget space and determines a second measurement value to be used as areference relative to the first measurement value of the oxygen sensor,said reference oxygen sensor being switched on at regular intervals forthe second measurement to prevent aging of the reference oxygen sensor,wherein, if the measured value for the oxygen concentration of theoxygen sensor deviates from the measured value of the oxygenconcentration of the reference oxygen sensor by a preset value, one ofthe oxygen sensor and the reference oxygen sensor transmits an alarmsignal.
 9. An apparatus as defined in claim 8, wherein at least one ofthe oxygen sensor and the reference oxygen sensor is integrated in theat least one suction pipe systems.
 10. An apparatus as defined in claim8, further comprising: a fan and fresh air supply; a control that isconfigured to set inertization levels in the target space, and controlthe fresh air supply and fan; and at least one detector to detect fireparameters in an air sample that is drawn from the target space by theat least one suction pipe system.
 11. An apparatus as defined in claim8, wherein at least one detector is integrated in the at least onesuction pipe system.
 12. An apparatus as defined in claim 8, furthercomprising: at least one CO or CO2 sensor to measure the air quality inan air sample that is drawn from the target space by the at least onesuction pipe system.
 13. An apparatus as defined in claim 12, wherein atleast one of the CO or CO2 sensors is integrated in the at least onesuction pipe system.
 14. An apparatus as defined in claim 8, wherein theoxygen sensors comprise electrochemical cells of zirconium dioxide. 15.A method for measuring the oxygen content in a closed target space formonitoring inertization levels in an inert gas device, the methodcomprising the steps of: drawing an air sample from the target spacewith one or more suction holes of a suction pipe system; monitoring COand/or CO2 content in the drawn air sample with a CO and/or CO2 sensor;and determining a first measurement value of the oxygen concentration inthe drawn air sample using an oxygen sensor; determining a secondmeasurement value of the oxygen concentration in the drawn air sampleusing a reference oxygen sensor, wherein the reference oxygen isswitched on at regular time intervals to prevent ageing of the referenceoxygen sensor; comparing the first measurement value to the secondmeasurement value; issuing a disturbance signal from one of the oxygensensor or the reference oxygen sensor when deviation of the firstmeasurement value from the second measurement value exceeds apredetermined amount; and supplying fresh air to the target spacedependent on a measurement value of the CO and/or CO2 content.